Plum tree not blooming well, or at all? Causes and solutions

Plum tree blossoms are beautiful – it’s frustrating (and worrying) when they don’t appear.

Most people think of the juicy stone fruit when they think about a plum tree, but they’re actually frequently planted for their beautiful flowers rather than their fruit. So if your tree’s underperforming in that department (which is quite common), it’s frustrating to miss out on what can be a beautiful springtime display or white or pink. And if you do want a crop of plums… well, no flowers also means no fruit, and that’s even worse!

So why do plum trees sometimes fail to bloom properly in the spring?

As a general rule, plum trees do not bloom until they are 3 to 6 years old, though varieties grafted on to mature rootstocks may do so after around two years. In established trees, improper pruning methods, spring frosts, suboptimal sunlight, irrigation and soil conditions may inhibit flowering.

I’ll break all of this down for you in this article. I hope to be able to answer all the questions you may have in a concise way. Read on!

First a little about plum tree species

Any answer to this question of plum tree blooming will be talking about Prunus americana (American plum), Prunus domestica (European plum) and Prunus salicina (Japanese plum). This article is addressing all three, based on their common features.

American plum is, unsurprisingly, the one that’s native to the USA and is typically planted more for its white flowers than for its fruit. European plum is not as widely cultivated in the USA, but gives a consistently delicious fruit.

In yards in the USA, you’ll most often find Japanese plum trees. Most commercially sold plums are of this species as well. Although they’re not said to be as consistently good as the European plum, they last longer before spoiling and therefore are ideal for transportation.

It has to be said that there is a particularly massive number of different cultivars and hybrids when it comes to plums, so many of the properties of the various plum types have become mixed and matched over time.

How old are plum trees when they start flowering?

young plum tree blooming
A young plum tree coming into bloom

Let’s do this one first.

It may not be your fault in any way! 3 to 6 years is a typical time period for a new tree to ‘mature’ – that is, start producing fruits or flowers. It doesn’t seem like a long time – and it certainly isn’t in comparison to some other fruit trees, such as mulberries (see this article) – but when you watch the seasons roll by year after year without so much as a petal, I find that, understandably, gardeners become inpatient or start to worry if something’s wrong.

There’s no speeding up this process, but it’s worth mentioning that if you’re planting another plum trees, dwarf varieties may bloom (and therefore have a shot at producing fruit) a year or two earlier.

Additionally, it depends on the propagation method that the nursery has used. Very frequently, the plum trees sold by nurseries and online are grafted, meaning they were grown from a small piece (called a scion) of another plum tree, which was transplanted on to another tree’s rootstock. This is a much quicker method of growing new trees than growing every one from seed.

This means that the young tree benefits from an already established root system and can mature more quickly. Grafted trees may produce flowers only a year or two after you plant them on your property.

It’s often possible to identify a grafted tree by looking for a visible line that separates the older rootstock and the rest of the tree, near the base of the trunk.

How does pruning affect plum tree blooming?

Pruning plum trees is a good idea – it helps maintain the tree’s shape, stimulates vigorous new growth and reduces the risk of over-long branches snapping as they become laden with heavy fruit in later life. But it’s the timing that’s important.

To encourage the best flowers, it’s a good idea to prune plum trees in mid or late summer. Why? If you prune earlier or later, you might be cutting off the very buds that will turn into flowers (and then fruit).

If you’re doing some light pruning, it is possible to identify which buds will turn into leaves, and which into flowers. The flowering buds are rounder and fatter, while the leaf buds are usually slim and pointed. Have a look at your tree at the right time of year and you’ll clearly see the two types. Just avoid the flowering ones.

Alternatively, you could prune in winter (which is the norm for most fruit trees), but the consensus is that mid or late summer pruning, even if you’re cutting off a few plums, is the best time. The other good reason to avoid pruning during winter dormancy is that plum trees are prone to silver leaf disease, a fungal ailment that can cause significant branch dieback. There are fewer spores in the air in summertime, which might otherwise infect the tree via the pruning wounds.

Weather and plum tree flowering

Cold weather preventing flowering

Plum trees are known for being quite ‘hardy’ – they’ll survive in cold weather. In the USA, they’ll usually grow in hardiness zone 4 or above, or some cultivars even in zone 3, close to the very northmost regions, especially the native Prunus americana. Check out the US hardiness zone map here.

However, cold snaps, if they occur at the wrong time, can still cause a plum tree to flower poorly in a given year. In spring, when new growth is just beginning, a sudden frost can kill off a significant proportion of delicate flowering buds, or cause new flowers to fall off early.

Can this be prevented? Plum farmers obviously have to get this down to an art if they don’t want their crop to be spoiled for the year, but you can easily do it yourself. This video shows a simple way to do it. You can use plastic, horticultural fleece or hessian. The minor effort will be worth it when you see those blooms coming and you can say “I did that”!

If your plum tree is growing in a container in spring, you should consider moving it to a sheltered porch or into a cool garage overnight, when a frost is predicted. You’ve got a keep an eye on the forecast though. I use an app that alerts me when the temperature’s expected to drop below freezing.

Warm weather preventing flowering

In the same way that there’s a limit to how much cold they’ll tolerate, plum trees also have their limits when it comes to heat. In general, the various cultivars will grow in even the warmer parts of the USA, sometimes even up to hardiness zone 10 (particularly the Japanese plum), but cooler weather in the winter is necessary as well.

Why? Cold temperatures in winter tell the tree that it’s time to drop its leaves and enter its dormancy phase, in preparation for another growing season. If there is an unusually warm winter and it doesn’t enter dormancy, its natural cycle is broken and it won’t produce flowers or fruit the following season.

This phenomenon is described in terms of ‘chill hours‘ – the total number of hours that a tree is exposed to temperatures below 45 °F/7 °C. Page 22 of this academic review outlines the chill hour requirements (CH) for numerous Japanese and European Cultivars. European plums varied from 579 to 1323 winter chill hours, while the Japanese plums needed 118 – 685, reflecting their slight preference for warmer climates. If you live in a warmer area in the states, it would be worth checking this reference map from the US Dept of Agriculture to see how many chill hours are normally expected where you live.

Year-on-year blooming variation

Another phenomenon that occurs in plum trees may be at play if you’ve got a poor show of flowers this year. Biennial bearing means a tendency for the tree to focus its energies on flowers one year, and fruits the next.

Think about last year – did you have a good year for flowers? If so, your lack of a good blossom this year it might be part of the tree’s biennial-bearing pattern.

This same issue occurs in many fruit trees, such as pear, apricot and avocado. Fortunately though, trees often seem to grow out of it – it’s more of an issue when they’re young.

Soil, sun, water and plum tree flowering

Plum trees certainly have their preferences for where they prefer to grow. There are several environmental factors that will affect the overall health and vigor of your tree. A poor display of flowers can be a key sign of tree stress. In plum trees, it’s best to try to identify this as soon as possible, or your tree will struggle through years of poor growth and bear minimal fruit.

In terms of soil, plum trees like two things in particular: that it’s mildly acidic (pH 6-7) and that it’s well-drained- fairly typical for fruit trees. This means clay-like soils that are in damp or waterlogged soils are likely to stifle its growth and therefore its flower and fruit production.

They also won’t flower very well if they’re planted in a shady spot. They prefer a position that’s fully exposed to the sun. American plum will tolerate light shade though, probably as it’s adapted to growing natively in more northerly regions.

Unless your tree is young enough to dig up and transplant to a more sunny or better-drained site (with the accompanying shock that often occurs to the tree) it may never bear flowers or fruit particularly well.

Plum trees don’t usually need much watering when they’re older unless they’re in containers. But if you have a younger tree, it’s actually quite important to monitor the soil’s moisture levels, because it’s much more vulnerable to drought. This isn’t as hard as it sounds though – just dig your finger a couple of inches into the ground near the tree. If the soil feels dry or it doesn’t stick to your finger, the soil needs water.

In practice, during dry spells, this will amount to a good 30-50 minute soak with a hose once a week. You’re trying to water the ground deeply, rather than just the top couple of inches, to reach the deeper roots.

Here’s an easy one that so many people neglect – It’s important to apply a good layer of organic mulch, such as bark chippings, around the base of the tree once a year. This provides a constantly decomposing source of organic matter, which insulates the roots and prevents them from drying out. A 3-foot radius around the trunk of mulch that’s a good 4 inches thick would be what I’d recommend – but keep it shallow just where it touches the trunk, as this can cause trunk rot.

Do fertilizers help plums to flower and produce fruit?

plums ripening on tree
Plums ripening in early July

You’ve probably noticed there are many different kinds of fertilizers on the market. But which ones will help flower production?

Most fertilizers will be labelled with something like ’10-10-10′. This refers to the proportions of nitrogen, phosphorus and potassium respectively, known as NPK. N, P and K are responsible for different parts of plant growth – in general, nitrogen for leaves, phosphorus for roots and shoots, and potassium for flowers and fruits.

Therefore a fertilizer with a higher ‘K’ ratio might be more effective. At my local nursery, they use tomato fertilizer for a lot of their flowering trees as it meets these requirements. But remember to adhere to the manufacturer’s instructions carefully. You can easily overdo it and cause harm to the tree.

It isn’t hard to test your own soil, to find out if it’s deficient in potassium. A good gardener knows his soil, right? I use the Rapitest soil testing kit at home and find it excellent – especially as it’ll tell you your soil’s pH as well.

I hope you found this article really helpful. Please have a look at my other posts!

This post contains original images from the author, plus those attributed to:

Appaloosa, CC BY-SA 3.0, via Wikimedia Commons

Syced, CC0, via Wikimedia Commons

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